Development of an on-line electrochemical analyser for trace level aluminium Original Research Article

An in-house designed computerised flow injection (FI) system for low-level aluminium analysis is examined. A simple, low cost electrochemical detection system has been implemented with computerised control and data acquisition system. The system consists of a commercial electrochemical analyser, FI components (manifold, pumps and valves) and an in-house designed control system to perform automated analysis. This system was developed to study aluminium speciation in water, particularly for drinking water. The analytical technique was based upon the complexation reaction between aluminium and a ligand—DASA (1,2-dihydroxy-anthraquinone-3-sulphonic acid). ‘Labile’ and total aluminium concentrations, Allabile and Altotal, respectively, were determined by measuring the sample before and after UV irradiation by amperometry at +0.6 V. The limit of detection for this technique was 10 μg/l (0.37 μM) and the linear calibration range was up to 1.6 mg/l (60 μM) with r2 value of 0.999. The Allabile/Altotal ratios of the water treated by 40, 80 and 100 mg/l of alum using a laboratory scale pilot plant to simulate conventional drinking water treatment processes were found to be 0.4, 0.5 and 0.8, respectively. These results indicated that when higher alum dose was employed, the residual aluminium was present mostly as the ‘labile’ species. Whereas, if the treatment process was not running at its optimum condition (underdosing), a large portion of aluminium was present as natural organic matter (NOM)—aluminium complexes in the treated water. The system offers a practical and effective means of providing extended knowledge of residual aluminium in drinking water.